This Instructable describes a very simple and inexpensive testing apparatus that middle school students can use to test model heart valves that they design and build. Students design and build simple heart valve models, then place then into this test setup. They then test both forward flow and back flow through their valves using glass beads as blood cell stimulants. This heart valve apparatus and the corresponding instructional unit was developed by a team of STEM Fellows at the Washington Alliance for Better Schools (http://wabsalliance.org) during the 2014-2015 school year. Team members included:
Ellen Smith, science teacher, Einstein Middle School, Shoreline, WA
Briahna Attebery, science teacher, Einstein Middle School, Shoreline, WA
Tamara Haberlack, science teacher, Hidden River Middle School, Monroe, WA
Mariola Kulawiec, founder, Witty Scientists
Eric Lagally, science instructor, Western Governors University
Chris Skilton, Seattle & King County Public Health
To view and download the entire unit, including a comprehensive summary, lesson plans, presentations, and assessments, please view the WABS site here: <link coming soon!>
Step 1: Purchase the Components
To build this test setup, you will need to purchase two main components. The first is lengths of clear acrylic tubing with an outer diameter of 3.5". While there are several vendors for this type of material, the least expensive tend to sell the tubing in lengths of 6 feet. Each test apparatus requires two 6-inch lengths of tubing, so it is possible to construct 6 test setups from one 6-foot length.
The second component is a standard 3" plumbing coupling, made from either ABS or PVC. The couplings are labeled "3-inch", but actually have an inner diameter of 3.5", which matches the outer diameter of the acrylic tubing. These couplings are commonly available at home centers (Home Depot, Lowes, etc.) for between one and two dollars per unit. The PVC couplings are white in color, while the ABS couplings are black in color. In principle the material does not matter, although in practice the ABS couplings have a slightly larger ring in the center of the inner diameter of the couling, which makes an easier ledge for students to place their valves onto.
We recommend that you plan to construct one testing setup for every 5-6 students in a class. Our classes worked best with between 6 and 8 test setups.
Step 2: Cut the Tubing
There are several ways to cut the acrylic tubing, but it is important to use a cutting instrument with fine teeth so as not to leave too rough a surface. This reduces the amount of sanding required later. Suggestions for tools to use include table saws, band saws, or hand saws with a miter box. The latter option is the most inexpensive but still provides good results.
Secure the tubing in the miter box and cut slowly, to avoid overheating and melting the plastic. It should take between two and three minutes to complete a cut.
Step 3: Smooth the Cut Ends of the Tubing
Since the tubing will be handled by small hands, it is important to smooth the tube ends to avoid cuts. Stand each tubing section on its end and move it in circles on a piece of 400-grit sandpaper. 45 seconds of sanding (60 circles) is usually sufficient. Be sure to sand both ends of each tubing piece.
Step 4: Sand the Inner Diameter of the Couplings
The fit between the couplings and the tubing is usually too tight to allow students to remove the tubing themselves, which is necessary to insert and remove their valve models. To widen the inner diameter of the couplings, it is necessary to sand them using a rotary sanding attachment chucked into a hand-held power drill. These sanding attachments can be purchased in home centers or woodworking stores.
Be sure to move the sanding attachment in circles along the inside edge of the coupling, opposite the direction the bit is rotating. This ensures rapid material removal.
You should wear proper safety equipment for this step, including safety glasses and a dust mask. Ensure adequate ventilation while you are sanding, and use a dust collection mechanism of some sort if you have one.
5 minutes of sanding is usually required for each coupling. Test the fit of the tubing into the coupling to ensure it is easy to insert and to remove.
Step 5: Wash and Dry All Parts
The tubing and the couplings will be covered with fine plastic dust at this point. Before use, wash all parts in water and dry thoroughly. Test the fit of all parts again to ensure they can be easily separated by middle school students.